Carbon black is produced by the pyrolytic decomposition of hydrocarbons, typically in the form of oil introduced into a stream of hot combustion gas. The pyrolytic reaction takes place in a refractory tubular structure known as a reactor.
Commercial production of carbon black generally occurs in either of two different kinds of reactors, the tangential reactor and the axial reactor. The names describe the flow patterns of combustion gas within the reactor. Both kinds of carbon-black reactors are known to those skilled in the art. Generally speaking, the axial-flow reactor is preferred for making carbon black intended for certain uses, particularly those uses where control of particle size distribution of the carbon black product must be maintained within certain relatively narrow ranges. For example, tire companies require carbon blacks with a very narrow particle size distribution for manufacturing racing and high-performance tires, where traction of the tires is a primary requirement. Carbon blacks used for making racing tires thus must have a relatively narrow particle size distribution (also know as "tint", a numerical factor which increases as the particle size distribution decreases).
Carbon blacks having a relatively narrow particle size distribution have heretofore been produced by an axial reactor with one or more flows of feedstock oil radially introduced into the stream of hot combustion gas. This arrangement causes a relatively rapid dispersion of the oil in the gas stream and thus pyrolyzes all the feedstock oil under substantially the same thermal condition, i.e., at substantially the same location within the reactor. Radial introduction has been the normal way of achieving quick mixing of the oil with the hot gas and a resulting short flame within the throat of the reactor, which yields a carbon black with very narrow particle size distribution, i.e., higher tint for the same surface area and structure of the carbon particles. Carbon blacks used in certain other applications should have a lower tint, that is, a wider particle size distribution. Such carbon blacks are produced in reactors designed to increase, rather than minimize, the reaction time of the feedstock, but the use of different reactors for the two kinds of carbon blacks is costly. Nevertheless, there is a need for carbon black with higher tint than commonly available with the conventional radial-injection axial reactor. Moreover, radial injection of the feedstock oil into the conventional reactor of circular cross-section can cause grit and erosion of the reactor inner wall if injection pressure and axial gas velocity are not properly balanced.